Zuma with a soft and flexing hull

I have a 1985 Zuma I just picked up and it seems to me the hull is really flexable compaired to my sunfish.
Just the weight of the empty boat on the trailer bunks makes a slight indentation in the hull.
Is this normal or has the hull gotten weak over time? I can't decide if I should cut access ports and try to beef up the glass from the inside or just junk the hull and sell the parts.